Spark plug suppressors can help suppress or reduce electromagnetic interference (EMI) and/or radio frequency interference (RFI), which may be by-products of an ignition spark when the spark plug is used in an internal combustion engine. The EMI and/or RFI may interact with engine control systems and/or other on-board electronic devices, so reducing the EMI and/or RFI may be desirable in some instances. Additionally, spark plug suppressors may help seal one or more spark plug components such as the center electrode, terminal, or both within an axial bore of the insulator.